Optical fibre switching assembly

ABSTRACT

An optical guide switching assembly in which steering devices are used to assembly deflect radiation from a transmitting guide to a selected receiving guide. Each of the steering devices includes a collimator light emerging from the transmitting guide and an actuator to cause relative movement between the collimator and the guide to cause the deflection, or to move the guide and collimator together. The actuator can be piezoelectric and of either a foil type, or a monolithic type, and mechanical leverage can be used to improve deflection. Capacitive sensing means provide positional information for feedback control, preferably in a diagonal switching arrangement.

[0001] This invention relates to an optical guide switching assembly andto steering devices used in the assembly for deflecting radiation from atransmitting guide in order to direct the radiation to a selectedreceiving guide.

[0002] One of the major problems facing the invention is to providerapid switching with low insertion loss (high coupling efficiency andlow cross talk) for high port counts, whilst evolving a compact designwhich can be readily manufactured. A related problem is to increase theswitching capacity of an optical fibre switching assembly, without theexpense of an increase in physical size. At least preferred embodimentsof the invention have been especially designed to deal with theseproblems.

[0003] According to the main aspect of the invention, an optical beamswitching assembly comprises:

[0004] (a) a first set of optical guides spaced from a second set ofoptical guides, and

[0005] (b) respective steering devices for causing deflection of a beamof optical radiation from a selected transmitting guide in the first setso that it is received by a selected receiving guide in the second set;

[0006] characterised in that each of said devices comprises collimatingmeans for collimating light from said transmitting guide and means formoving said collimating means or for causing relative movement betweensaid collimating means and said transmitting guide to cause saiddeflection.

[0007] Advantages of the latter arrangement include greater deflectionfor a comparatively smaller movement (of either the collimating means,or the transmitting guide) and higher switching speeds due tocomparatively lower inertia. For example, in the case where an endportion of optical fibre is subject to transverse movement to deflect anemergent beam, the end portion has less inertia and a wider deflectionis possible at higher speed. This is also beneficial in designing aswitching assembly having a high packing density of (e.g.) opticalfibres.

[0008] The optical guide can be, for example, an optical fibre whichconducts layer light, or a waveguide made of silicon or other dielectricmaterial which conducts infrared light. These guides. (for example,optical fibres), can be arranged in the switching assembly so thatemergent beams of radiation are projected directly across a space, i.e.between separated sets of transmitting and receiving optical fibres.Alternatively, they can be arranged in the same array where beams ofradiation are projected from sets of transmitting optical fibres to areflector, which then reflects the beams back to receiving opticalfibres. (Reference made herein to optical fibres is by way of, exampleonly and can be taken to cover other forms of optical guide.)

[0009] The steering device can include, for example, a piezo electrictransducer for deflecting an end portion of a transmitting fibre so thatthe radiation (which exits from the fibre) is caused to move in thefocal plane of a collimating lens. Alternatively, the end of thetransmitting fibre can be fixed and a collimating lens can be moved withrespect thereto, so that the focal plane of the lens is moved around theend of the fibre to produce the same effect. Alternatively, the end ofthe transmitting fibre can have a collimating lens either integraltherewith, or attached thereto, so that the fibre and the lens can movetogether to produce the same effect.

[0010] Instead of using a piezo electric transducer, electrostaticdeflection means can be used either to move a fibre with respect to afixed lens, or to move a lens with respect to a fixed fibre. Forexample, the surface of the end portion of the fibre can be metallisedor given sonic other conductive coating, so that it forms oneelectrostatic movable “plate” which co-operates with fixed electrostatic“plates” adjacent the movable “plate”.

[0011] Where a piezo electric transducer is used to cause movement, itcan be of a “foil type”, where fingers of a comb-like array of piezotransducers are attached to actuating members, such as foil strips, forproducing orthogonal displacement of either the optical fibre or theleas system. Such foils and combs can be assembled in a laminar matrix.

[0012] Alternatively, the piezo electric transducer can be of a“monolithic type” where each transducer is made of piezo electricmaterial, it has a body with a longitudinal axis, and the body hasconductive strips aligned with said longitudinal axis so as to definerespective portions of the piezo electric transducer which are energisedto impart respective transverse movements in different radialdirections. This provides a resultant motion in orthogonal axes. Amultiplicity of such bodies can be assembled in a columnar matrix. Thebody can have a bore aligned with its longitudinal axis in which thefibre is received, whereby bending of the fibre occurs with respect tosaid longitudinal axis. Alternatively, the body is attached to thecollimating lens which moves relative to a fixed fibre.

[0013] This “foil type” and “monolithic type” which are described inmore detail below, can be designed to provide greater beam deflectionthan prior art arrangements, with less inertia, to achieve more rapidswitching between a greater number of fibres and also to provide ahigher packing density of fibres.

[0014] Preferably, position sensing feedback means are employed forsensing the amount of movement and for providing a feedback signal. Thisis used in a control system which energises the transducers to ensurethat the transmitted radiation is aimed at the correct receiver fibrefor making the required switching connection.

[0015] Preferably, a capacitive feedback system is used. For example,the fibre end has a conductive coating (as one “capacitor plate”) and itmoves with respect to fixed conductive tracks (acting as the other“capacitor platen”). The term “capacitor plate” applies generally to anymember, surface, or structure which, together with the intervening“dielectric” (which could be air, a liquid or gaseous fluid, or someother dielectric material), forms a good capacitive coupling betweenfixed and moving elements. Such “plates” can therefore take variousforms, e.g. they can be flat, curved or parts of some structure havingsome inherent capacitive properties. In another example, a lens systemor optical collimator, having an associated “capacitor plate”, moveswith respect to a fixed fibre end, having an associated “capacitorplate”.

[0016] In a preferred embodiment of the invention, conductive tracks oninsulating boards are arranged in layers to form one set of fixedcapacitive plates of a position sensing feedback system; the moving endportions of respective fibres having conductive coatings to form theother plates. Alternatively, a conductive plate moves with a lens, andanother conductive plate is fixed with the fibre. These tracks can crossorthogonally so that pairs of conductive tracks, associated withindividual fibres, can be polled or addressed so as to sense the changein capacity proportional to the relative displacement between the fibreends and the lens systems. In a preferred embodiment, a diagonaladdressing system is used which can be selectively energized andswitched in order to detect an instantaneous capacitive value relatingto the amount of beam deflection.

[0017] When using the monolithic type of (piezo electric material)transducer, its rod-like form may be comparatively short and thickwhereby bending is limited with respect to the longitudinal axis. Inthis case, mechanical leverage means can be used so as to magnify thetransducer movement before imparting motion to cause relative movementbetween the collimating lens and the end portion of the fibre, or tomove the end portion of the fibre to which a collimator lens is attachedor forms an integral part. Preferably, such leverage means includes agimbal mounting and an extension rod located between the end of die bodyof the piezo electric material transducer and a point on the gimbalspaced from its pivotal axis. In the latter case, where the collimatoris part of or attached to the fibre end, the gimbal mounting ispreferably on the body of the collimator to provide optimum deflectionof the emergent beam.

[0018] Embodiments of the invention Will now be described with referenceto the accompanying drawings in which:

[0019]FIG. 1 is a schematic cross section through one embodiment of afoil type of device for moving optical fibres;

[0020]FIG. 2 is a similar cross section through a monolithic type;

[0021]FIG. 3 is a perspective view showing foil actuating strips (drivenby piezo electric material actuators) supporting fibre optics;

[0022]FIG. 4 is an elevational cross section to a foil typesub-assembly;

[0023]FIGS. 5 and 6 are different perspective views of a 4-port switchassembly, including 4 lenses, showing piezo combs connected to foilstrips for moving optical fibres in the focal plane of lenses (only 4ports are shown to simplify explanation, since multiplicity of portswould be employed in practice);

[0024]FIGS. 7a-7 d are perspective views showing the stages ofmanufacture of a monolithic type of actuator, and FIG. 7e is a planview;

[0025]FIG. 8 shows a group of monolithic actuators and lenses;

[0026]FIG. 9 is a schematic elevation through a monolithic actuatorassembly with a lens array (when a hexagonal array of fibres andactuator is used);

[0027]FIG. 10 shows the subassembly of FIG. 9 used in a reflective typeof switching assembly in which radiation is projected through ahalf-silvered mirror onto a CCD;

[0028]FIG. 11 shows the subassembly of FIG. 9 used in a pass-throughtype of switching assembly in which radiation passes directly fromtransmitter fibres to receiver fibres and FIGS. 11a and 11 b arediagrams for further explanation;

[0029]FIG. 12 is a schematic cross section illustrating a capacitivesensing arrangement;

[0030]FIGS. 13a-13 b show another embodiment of capacitive sensing;

[0031]FIG. 14 is a schematic electronic diagram;

[0032]FIG. 15 shows a technique of diagonal switching explained indetail below;

[0033]FIG. 16 shows fibres with attached and integral collimator lens;

[0034]FIG. 17 shows collimator arrangements with monolithic types;

[0035]FIG. 18 shows a gimbal mounting for a collimator;

[0036]FIG. 19 shows an alternative gimbal mounting;

[0037]FIG. 20 shows an exaggerated effect of tilting the gimbal mountingand collimator;

[0038]FIG. 21 shows a detail of a foil type connection structure forgimbal and translational mounting of collimators;

[0039]FIG. 22 shows an array of piezo tube type actuators on atriangular array;

[0040]FIGS. 23a and 23 b are side views of an embodiment using a movinglens and a fixed fibre;

[0041]FIG. 24 is a isometric view of the latter embodiment using amoving lens and a fixed fibre;

[0042]FIG. 25 shows a group of the arrangement of the devices shown inFIG. 24;

[0043]FIGS. 26a-26 e shows an example of each of five different foildesigns in plan view for a five-layer 64 port foil type switch assembly;

[0044]FIG. 27 is a perspective view of a piezo comb actuator; FIG. 27ashows a detail of the electrical connectors and FIG. 27b showsconnection details for the piezo comb actuator of FIG. 27a;

[0045]FIGS. 28a-28 e show different plan sectional views of each of 5layers of piezo comb arrays and foil arrangements;

[0046]FIG. 29 shows a sub-assembly (foil type) of a switch (including 64ports), and

[0047]FIG. 30 shows a rear view of the switching sub-assembly (foiltype);

[0048]FIGS. 31a-31 c are isometric views of a sub-assembly of monolithictype actuators;

[0049]FIGS. 32 and 33 each show other switching assemblies; and

[0050]FIG. 34 shows two of the assemblies of FIG. 39 used with spacedtransmitter and receiver fibre sets.

[0051]FIG. 1 schematically illustrates “foil type” devices which can beused, for example, for moving optical fibres. In each device, piezoelectric transducer elements 1 a, 1 b, 2 a, 2 b form respective sets offingers of a comb structure fixed at one end to a support unit 3. Theends of the fingers are fixed to respective foils 4 a, 4 b, with pairsof comb-like structures located on opposite sides of respective fibres 5a, 5 b. Each fibre, such as fibre 5 a, is fixed to respective foil sets4 a, by a bead of adhesive 6 a or solder contacts if the fibre ismetallised. The piezo electric material transducer elements 1 a, 1 b, 2a, 2 b bend (in parallel) in the same direction so as to impart“push/pull” movement to the respective fibre (in one of two orthogonaldirections). Other piezo electric material transducer elements (notshown and which are arranged perpendicularly to the former elements)bend similarly (but in a different orthogonal direction so as to impart“push/pull” movement to the respective fibre. The resultant provides thefibre with two degrees of motion in orthogonal directions. Accordingly,radiation passing through the fibre 5 a and leaving from the end 5 a′can be deflected anywhere in an x-y plane. The “radiation” can be laserlight, or light from an LED, for example, but it can also be other formsof electromagnetic energy.

[0052]FIG. 2 schematically illustrates a “monolithic type”, where eachof the piezo elements 7 a, 7 b has a cylindrical or rod-shaped body witha central bore along its longitudinal axis in which the optic fibre 5 a,5 b is received. One end of each piezo element 7 a, 7 b is firmlysecured to support unit 3, and the free end is free to move as a resultof bending of the body with respect to the longitudinal axis (asexplained below). The drawing also shows electrical interconnects 8 a, 8b to the piezo elements. As with the foil type, radiation leaving theend 5 a′ is deflected by bending the fibre 5 a in the x-y plane.

[0053]FIG. 3 shows an enlargement of a modified “foil type” in moredetail. In this case each foil is in the form of strips, such as 9 a, 9b extending perpendicularly to each other and terminating at one end ina pad 9 c through which fibre 5 a passes and is sensed by the adhesivebead 6 a or solder contact if the fibre is metallised. FIG. 3illustrates three different arrangements, i.e. where the strips 9 a, 9 bjoin the pad 9 c at different locations (and in one case where strip 9 bis formed through two right angles before being joined to the pad. Theother ends of the strips are attached to the fingers 2 c, 2 d of a comblike structure of piezoelectric material. These fingers impart motion ineach of two respective orthogonal directions x-y (as shown) to the foilstrips, whereby the end portion of the respective fibre 5 a moves inthese directions, so that light emerging from the end faces 5 a′, 5 b′,5 c′ is deflected.

[0054]FIG. 4 is a cross-section, in elevation, (rotated through 90°),showing a set of optical fibres 5 passing through support structure 3,each fibre being secured to respective foils 9, arranged in separatedlayers, in a foil stack (not shown in detail). Each of the foils isconnected to respective fingers of a piezo electric comb structure 2 e,which is mounted in a support plate assembly 3 a in the supportstructure. Ribbon cable 10 is connected to the piezo actuators toprovide energization.

[0055]FIGS. 5 and 6 illustrate, more graphically, how the piezo electricmaterial comb structures 2 e are connected to the foil structures 9,which are attached to respective optic fibres 5, whereby the ends of theoptic fibres are caused to move in the focal plane of respective lenses12. FIGS. 5 and 6 show schematically a 4 port structure having only fourlenses, in order to simplify the drawing and explanation. The assemblycan, of course, have “n” lens elements for “n” fibres in an “n” portswitch, where “n” is the number of ports required in the particularapplication. The lenses 12 are supported in a block 13 which alsosupports capacitive position sensors (as explained below).

[0056]FIG. 7 shows four stages 7 a-7 d during the manufacture of a“monolithic type” of piezo electric material transducer. The first stage7a illustrates a body 7 of piezo electric material having a generallycylindrical shape. The second stage shows pairs of V-shaped saw cuts,V1, V2, V3, which form grooves defining a central pillar 14 oftriangular cross-section segments 15 a, 15 b, 15 c and peripheral thinpillars 16 a, 16 b, 16 c, each of triangular cross-section. Thesegrooves are then filled with a low-melting point alloy 17 in stage 7 c.Finally, further saw cuts S are made as shown in FIG. 7d in order todefine three interconnects in the form of isolated conductive pads 18 onthe triangular sides of the central pillar 14. These pads are isolatedalong the length of each side edge due to the gap 19 (of piezo electricmaterial) which is opened up by the respective saw cut S. Electricalinputs to each of these pads cause the central pillar 14 to bend and toflex the fibre optic. The plan view of FIG. 7e shows the individualmotion “d” imparted by each pad 18 when energised. By suitableenergization of these pads, a resultant motion can be achieved formoving the pillar 14 in the x-y axes. A through hole 20 bored in thebody of piezo electric material, along the longitudinal axis, receivesthe optic fibre as shown in the schematic diagram of FIG. 2.

[0057] A similar structure can be made by (a) moulding the pillar 14 ofpiezoelectric material prior to firing and (b) attaching the pads 18 bycoating. Such a pillar could be hollow or solid and of differentcross-sectional shapes.

[0058]FIG. 8 is a perspective view of a group of monolithic typetransducers 7. Each of these transducers supports a respective opticfibre 5, the terminal end of which moves in the focal plane of therespective lens 12. This shows the fibre array in a hexagonal/triangulararrangement, but square arrays can also be used.

[0059]FIG. 9 is a cross-section through three monolithic transducers 7,each mounted on a base board 3 which supports optic fibres S. These areshown as having adding 19 on the lefthand side of the board 3 and asfibres extending through transducers 7 which terminate in ends 7 a closeto each collimating plano-convex lens 12 of a lens array. A bi-convexlens array can also be used. This separation is indicated by the gap 21,which is arranged so that light emerging from the end of each fibre isat the focal plane of the respective lens. Connectors 20 having bondwires connected to transducers 7 are also shown.

[0060]FIG. 10 is a schematic view of an assembly used in calibrationduring setting up. It shows beams of light 22 output from each of thelenses 12 which first pass through (e.g.) a partially reflective mirror(e.g. dielectric multilayer stock or half silvered) 29, which partiallytransmits beams to a CCD device 23 and partially reflects the beams. Theposition of the straight through beams on the surface of the CCD 23 canbe related to the absence (or presence) of signals used to energise thepiezoelectric transducers. Likewise, the position of a deflected beamfrom a transmitter fibre, which is partially reflected by the mirror 29onto a receiver fibre (in the same stack), as well as partially incidenton the surface of the CCD 23, can be related to instantaneous signalsused to energise the piezoelectric transducers to cause differentdeflections. This enables the transducer drive signals to be derived forcorrectly aiming and steering the end portions of the fibres so that theoutput beams arrive at their correct destinations (i.e. the selectedreceiving fibres in the working switch). For example, lookup tables canbe used to number the ideal fibre-tip positions at each end in order tocreate required fibre-to-fibre couplings (i.e. cross-connections betweentransmitter and receiver ports. This enables operation of the assemblyas a switch and the assembly would be made reversible (i.e. thetransmitter fibres can be the receiver fibres and vice versa).

[0061]FIG. 11 shows a different arrangement which can be similarlycalibrated but also used in operation, and where the beams of light 22leaving the transmitting collimating lens assembly 12 t are received bya receiving lens assembly 12 r, which focuses the light on respectiveoptic fibres 5 in a (similar) monolithic structure. The energisingsignals can be similarly calibrated with regard to beams of lightpassing straight through, and being deflected, since the transmittingbeams will be received by respectively different fibres. Thisarrangement is fully “reversible”, since the “transmitters” can be the“receivers”, and vice versa.

[0062] Referring to FIG. 11a, it is to be noted that:

[0063] i. Each fibre in the switch is associated with a smallcollimating lens

[0064] ii. Fibre tips are placed in the focal plane of each lens

[0065] iii. A collimated Gaussian beam will be produced if a fibre islit since light will emerge from the fibre tip in the focal plane and becollected and collimated by the lens

[0066] iv. Movement of each fibre-tip within the focal plane results inan effective angular swing of the collimated beam

[0067] v. By symmetry, any collimated beams which arrive at a targetlens will focus to a point in the focal plane of the target lens

[0068] vi. If a fibre-tip were placed at the point defined in (v) thenlight will be coupled into the fibre

[0069] A combination of (iii) and (vi) permits fibre to fibre coupling.Light from one fibre can be transformed into a directional collimatedbeam by (iii). By moving a lit fibre-tip (the “source”) it can bearranged that the collimated beam from its associated lens is directedas the lens associated with a totally different fibre (the “target”). Bymoving the target fibre it can be arranged that light from the incomingcollimated beam may be collected and thus a fibre-to-fibre couplingcondition has been set up. Since the optical system is symmetrical, theterms “source” and “target” fibre-tips can be used interchangeably andin a coupled scenario light can be transmitted in either direction.

[0070] Calibration would be carried out using the following steps:

[0071] 1. Each fibre is ground in 2D and for each fibre the capacitancevalues for retro reflection are located

[0072] 2. Sequentially each fibre is moved to the positions on the CCD,using the retro reflection to calibrate the reference points.

[0073] 3. For each fibre to each fibre the 2x and 2y average voltagesare optimised for maximum coupling

[0074] 4. With 128 fibres (64 at each end) we have 64 x/y capacitancevalues stored, i.e. 16,384 numbers. These are stored in the non volatilememory of the switch and used as the target capacitance values for thedesired switch settings.

[0075] These steps refer to either the reflective or otherstraight-through design.

[0076] Referring to FIG. 11b, there exists an optimum rest position offibre-tips which confers important system benefits (including optimumcoupling efficiency).

[0077] With no effective deflection (i.e. no applied voltage on thepiezo actuators), the collimated beam from each fibre tip should ideallyaim towards the centre of the target lens array (or, by reflection, tothe centre of the source array in a folded system). The aim of this isto minimise the bipolar fibre-tip translation required (from the restposition) to approximately one half of the array size.

[0078] Fibre tip Z positions must be within the depth of focus of thelens array to ensure high quality collimated beams. All fibre tips mustbe within a range behind the back surface of the lens array glasssubstrate, defined by the focal length of the lens array.

[0079] The angle of fibres relative to the lens array should be ideally90°. Any significant deviation from a perpendicular geometry may have adetrimental effect on coupling efficiency and limit scalability.

[0080] In order to sense the position of each individual optical fibre,foil type or monolithic type (for correlating deflection with transducerdrive signals), capacitive coupling is employed between (e.g.) eachmoving end portion of the fibre optic (which is coated with conductingmaterial to form a moving plate), and other relatively fixed plates. Anarray of such coated fibre optics can be aligned inside a similar arrayof capacitive sensor pickup units. The array may be either square orhexagonal to ensure optimum packing density. Array sizes are scalable tolarger number of fibres (>1000) suitable for future high port countoptical cross connects for fibre optic communication applications.

[0081] The position of the optical fibre is determined by a measure ofthe capacitive coupling between the fibre and capacitive sensor plates.As capacitive feedback determines the fibre optic position with respectto the leas array 12, the capacitive feedback mounting unit is rigidlyconnected to the lens array to ensure precise reference to the fibres tothe lens centres. (An alternative embodiment uses fixed fibres and amoving lens). The capacitive sensor plate pickup units can be formedeither as shown in FIG. 12 or in FIGS. 13a and 13 b.

[0082]FIG. 12 shows, in plan view, one method, where the sensor pickupunit formed from through-hole plated holes in an insulating boardmaterial 30. The insulating board material may be printed circuit boardor some alternative insulating material such as ceramic. The sensorholes are segmented into four isolated quadrants designed “North”,“South”, “East” and “West” (N, S, E & W). Electrical contact is made tothese with appropriate patterned electrical tracks 31N, 31S, 31W, 31E.Each (coated) optical fibre passes down the centre of the sensor hole.

[0083]FIGS. 13a and 13 b show, in sectional view, an alternativearrangement in which the N, S, E and W capacitive sensor plates areformed by perpendicular arrays of parallel conductive tracks 31N, 31S,31W, 31E intersecting an array of holes through which the optical fibres5 pass. The capacitive sensor tracks for NS and EW detection arearranged in parallel arrays, the two parallel arrays being perpendicularto each other. For isolation, the NS & EW sensor arrays are isolatedfrom each other by sandwich layers of insulating matrix material 33.Ground plane layers 32 above and below each sensor layers act as ascreen against environmental electromagnetic pickup. Note that FIGS. 13aand 13 b show only two layers of NS and EW sensor tracks. Improvedcapacitive feedback sensitivity may be achieved by increasing the numberof sensor tracks (layers).

[0084] The arrangement of FIG. 12 results in a larger capacitivecoupling between the fibre 5 and the sensor plates, whereas that ofFIGS. 13a and 13 b is inherently easier to manufacture (but to achievesufficient capacitive coupling between the NS and EW sensor tracks, avertical array of such tracks are required).

[0085] An AC voltage is applied to the conductive coating on eachoptical fibre, typically at audio frequency. The resultant ac voltagecoupled to the sensor plates is then detected using an appropriate lownoise amplifier circuit, such as that shown in FIG. 14 (where similarcomponents are identified by similar reference numerals). The ac voltagegenerated on the sensor plates is proportional to the capacitivecoupling between the sensor plate and the fibre conductive coating. Thisdepends on the local distance of the fibre to the sensor plate.Combining information from 31N, 31S, 31E and 31W plates therefore givesinformation on the localised position of the fibre.

[0086] Increased positional accuracy is achieved by coupling thedetected voltages on the N and S sensor plates to the two inputs of adifferential low noise amplifier 35. Thus as the optical fibre movescloser to the N plate, the N plate detected signal increases, similarlythe detected signal on the S plate decreases. The differential isapplied to the amplifier. A similar arrangement is used for the SWplates.

[0087] To enable the unique positions of individual fibres within largearrays of optical fibres to be detected, an AC signal needs to beapplied to each fibre. Such an arrangement is not practicable with largenumbers of fibres. We therefore prefer to use a method by which theunique positions of arrays of fibres may be detected by selectivelyswitching between diagonal rows of such fibres. Details are shown inFIG. 15. By sequentially applying AC to the diagonal rows and bysequentially reading capacitive feedback signals from horizontal rowsand columns unique addressing can be achieved. This will now bedescribed in more detail below. (This diagonal switching can be usedindependently, i.e. in other switching assemblies.)

[0088] An AC excitation signal is applied to diagonal arrays of fibres(as shown in FIG. 15). For a 64 fibre switch array, there are 15 suchdiagonals, but by using a vertical and horizontal array of capacitivefeedback sensor tracks, arranged orthogonally, the number of addressablediagonals is reduced to just 8. This is explained with reference to FIG.15, which shows a 64 element array, but the following analysis isapplicable to any scalable array. In FIG. 15, the diagonals are A, B, C,D, E, F, G and H. Horizontal rows 0, 1, 2, 3, 4, 5, 6 and 7 such that,for example, the third fibre down from the top and the fifth from theleft is designated C2.

[0089] Diagonal array A utilises all 8 fibres along the diagonal.However, diagonal array B utilises 7 such fibres (B0 to B6), thisdiagonal is therefore connected to fibre B7 (bottom left corner).Similarly diagonal C comprises six such fibre elements (C0 to C5) andthis is connected to fibre elements C6 and C7. The process is repeatedso that all diagonals comprise 8 elements. (However, this connectionsystem can be scaled to any size of array). For example, a 256 fibrearray comprising 16 rows and 16 columns would be connected using 16diagonals. A generalised N fibre array therefore contains square root(N) diagonals.

[0090] Referring to the 64 fibre array shown in FIG. 15, the 8 rows and8 columns of the orthogonal capacitor sensing tracks are each connectedto 8 parallel differential amplifier detection circuits, such thatcapacitants is sensed along all rows and columns simultaneously; 1detection circuit per row and 1 detection circuit per column. Thecapacitor tracks need not be orthogonal, alternative angles can be usedas long as the tacks cross. As the excitation signal is applied alongthe diagonal and to only one diagonal at a time, only one unique elementin a row or column generates a capacitive feedback signal when detectedby the capacitive feedback circuitry. Thus for the present case of 64elements, for each diagonal excitation, 8 capacitive feedback signalsare read in parallel from each row and column. The outputs are connectedto an 8 channel ADC unit, one for the rows and one for the columns.

[0091] Note also that for very large arrays, the time to sense allelements with the capacitive feedback system is limited by the timetaken to excite and scan each diagonal. Improved switching time can beachieved by sub-dividing larger fibre arrays into sub-sections, where,for example, a 256 element array can be split into 4 smaller separatereadout arrays. This approach is scalable to any array size.

[0092] In order to provide a further improvement, a collimating lens canbe attached to or integral with the end of the optical fibre to providea wider angular spread of the emergent beam. In this case, both the lensand fibre move together which simplifies the design enabling rapidswitching speed for a high port count. These collimating lenses can beused independently i.e. with other switching assemblies, but they areespecially useful when used together with the miniaturised “foil type”or “monolithic type” of piezo electric material transducers describedabove.

[0093] As the fibre end and lens array can both result in backreflection (even when all faces are coated with mid-layer dielectricreflection coatings), some signal loss is incurred. Furthermore,coupling efficiency between fibre ends and collimating optics iscritically dependent on maintaining the position of the fibre end withinthe focal plane of the lens. Collimated fibre optics can be used to dealwith this problem. Insertion losses and back reflection within opticalswitch Systems can be considerably reduced and construction can besimplified by the use of collimated or integrally lensed fibre opticends (FIG. 16a and 16 b) in place of fibre optic ends and lens arrays.

[0094] Collimated fibre optics 40 are commercially available, theyincorporate a collimating lens 40 a attached to the single mode fibreoptic end portion 5.

[0095] Integrally lensed 41 fibre optics may also be used in place of acollimator 40 for all of the present applications discussed here.Integrally lensed fibre optics are formed by treating the fibre opticend in such a way that it forms a micro lens (integral lens fibre opticsystems are currently available from some manufacturers of fibre opticsystems). The advantage that both of these technologies provide in thepresent switching application is that the light emanating from the fibreoptic end is collimated and parallel without the incorporation ofadditional discrete optical components such as lens arrays.

[0096] Integrally lensed fibre optics may also be made by cementing anappropriate lens to the fibre end. In all cases coated or uncoatedcomponents may be used. Collimator based N×N fibre switches (i.e. Ninput port counts and N output port counts) have the advantage of lowinsertion loss, excellent cross talk performance, and excellentpolarisation independence.

[0097] Alternatively, fibre optic switching can be achieved in whichcollimated or integrally based fibre optic ends are incorporated intothe N×N switching matrix, thereby precluding the lens array 12 used inthe alternative switch structures described above.

[0098] Where capacitive feedback is used (as described above) todetermine the position of the collimator, the external surface of thecollimator is metallised or given a conductive thin film coating.

[0099] Connection to the collimator can be made using metallised fibresand capacitive feedback can be used to measure the capacitance betweenthe outer surface of the collimator rather than the metallised fibreoptic. However, if integrally lensed optics are used, capacitivecoupling is used to measure the capacitance between the sensor pcb andthe metallised fibre.

[0100]FIG. 17 shows schematically how the collimated or integral lens onthe fibre optic end can be incorporated into a monolithic piezo fibreoptic switch. This is one simplified solution in which the lens array 12is replaced by the collimator 40 or integral lens 41. Although not shownin FIG. 17, it is possible that the length of fibre between the top ofthe monolithic piezo actuator and the collimator may be increased.

[0101] To achieve greater angular swing of the collimated optics at theend of the fibre optic it may be mounted in a gimbals type mount 42 thatallows the collator 40 to pivot about its centre point as shown in FIGS.18-20, to provide movement in x-y axes 43. A flexure joint is preferablyused which is the collimator to the extension arm of the piezo actuatoras shown, for example, in FIGS. 19 and 21. Both gimbals and flexurejoints may be manufactured by a variety of means including patternedfoil. FIG. 21 shows how the use of foils coupled with a gimbalsarrangement may be used to tilt the collimated or integral lens fibreoptic end. In this case the gimbals arrangement may also be made using apatterned foil structure.

[0102]FIG. 19 and FIG. 20 show a variant of the collimator mountingscheme in which a tapered piece 44 forms an extension of the piezo tube8. The extension piece 44 provides mechanical advantage, i.e. itprovides greater XY movement of the collimator base than that generatedby the piezo tube scanner alone. The extension piece therefore givesmechanical advantage to the piezo actuator movement. (The exit beam isshown as 45 in FIG. 19). The piezo actuator extension rod 44 is taperedto reduce the resonant frequency of the mechanical system.

[0103] A key feature of this design is that the extension rod 44provides extra lateral movement in the XY plane (perpendicular to thefibre axis) of the base of the collimator than that provided by anunextended piezo actuator alone. The advantage of this is that thecollimated beam may be swung over a large, angular range for a givenpiezo movement. This is important as it provides a much wideraddressable range for the resulting beam emanating from the collimator,thus enabling much larger switch arrays to be built (i.e. larger N×Nswitch sizes—higher port counts).

[0104] With the monolithic type, the optical fibre passes through thecentre of the piezo tube scanner. The complete unit is replicated Ntimes for an N×N switch unit (FIG. 22)—note FIG. 22 shows only the piezoactuators—where the array may be either square or hexagonal/triangularin layout.

[0105] Individual piezo actuators are formed by moulding, firing and/orsubsequent sawing of the monolithic piezo material, followed bypatterning with electrical contacts.

[0106]FIG. 20 shows (in exaggerated schematic form), displacement of thefibre actuator assembly. The fibre optic is not shown in this drawing—itpasses through the centre of the piezo tube actuator 8.

[0107] The collimator gimbals and flexure mount could be manufactured ina number of ways, one route being patterned foils. FIG. 21 shows onepossible method of manufacture for the gimbals mount. Alternatively ameander type foil arrangement may be used to manufacture the flexuremount.

[0108]FIG. 23 shows an alternative embodiment of a monolithic type piezoelectric material actuator. In this case the fibre optic 5 (shown bentthrough a right angle) is held fixed in a mounting block 52 which alsosupports electronic interconnects and capacitive sensing plates(associated respectively with the fixed fibre and the moving lens).These sense lens displacement and provide a feedback control signal (asdescribed above). The lens 50 is supported by a lens mount 51 which isconnected to a monolithic type piezo electric material actuator via aconnecting lever 53. The isometric view of FIG. 24 shows a clearancehole 54 which enables freedom of movement. FIG. 25 shows a plurality ofthese actuators mounted on a rigid support plate and PCB 55 forproviding drive connections. As shown in FIG. 23a, for example, theextension rod 7 terminates in a tapered portion 53 and cylindricalrod-shaped portion 57 which is connected to lens mount 51. (see alsoFIG. 24). This arrangement is particularly advantageous becausecollimating lens 50 can have a conductive coating, to act as a capacitorplate and it is conveniently positioned with respect to the fixedmounting block 52, on which can be provided another capacitor plate(e.g. in confronting relationship), to provide positional feedbackinformation as a result of capacitive changes. Moreover, thisarrangement allows the components to be conveniently located on acapacitive sensing support structure, of laminar form, like thatdescribed with reference to FIGS. 13a and 13 b. This will also be moreapparent from the subassemblies shown in FIGS. 29 and 31-34 where thecapacitive sensing system includes flat conductive tracks, which areassembled in a laminar form, in a support structure or block, which canconveniently support other components of the switching assembly. Thisprovides both the advantages of capacitive sensing with a compact androbust structure which facilitates manufacture.

[0109]FIGS. 26a-26 e are plan views of an example of foil designs for a64 port foil type switching assembly. These are arranged in layers,insulated from one another, in the subassembly of optic fibre bundles.

[0110]FIG. 27 is a perspective view of a piezo electric comb structure2, for a foil type design of switch, showing sawcuts 60 separatingindividual actuators 1 and also showing metallised contacts 61, 62, 63.FIG. 27a shows how the fingers of the comb structure 2 are attached torespective conductive tracks of a flat flexible connector 2′. The piezocomb includes outer layers forming respective common +V and −V planesand an inner layer forming a control V place.

[0111] Referring to FIG. 27b, this schematically illustrates preferredbias-drive for enhancing the lifetime performance of the piezos. Thisessentially involves never driving either half of piezo bimorphs in sucha manner that they could otherwise be depoled. Bias-driving thusincreases device longevity. Another advantage is that the number ofelectrical interconnects to piezo combs can he drastically reduced.Essentially the top electrodes for all elements of the comb are madecommon, the bottom electrodes for all elements of the comb are also madecommon and only centre electrodes of the elements need independentcontrol. Thus, for a comb of 8 bimorphs, there are only 8+2 (10)electrical interconnects, rather than 8+8+8 (24).

[0112]FIGS. 28a-28 e show plan views Of each layer of piezo-comb arraysand foil arrangements such as those shown in FIGS. 26a-26 e. These areassembled into a switching assembly as showing in FIGS. 29 and 30. FIG.29 shows a 5 foil stack 64, piezo combs 2 in a support plate 65 to whichelectrical connections are made by ribbon cable 66, the components beingmounted in a support structure 67. An optic fibre array 5 passescentrally through structure 67, as shown also in the rear view of FIG.30.

[0113]FIGS. 31a and 31 b are cut-away perspective views of a monolithictype of switching array in which monolithic tube type piezo actuators 70deflect metallised fibre optics 71 that terminate in (or adjacent)collimators 72 mounted in a capacitive sensing feedback board 73;mechanical leverage (like that shown in FIG. 20) being applied by theextension levers 74 (an enlarged view being shown in FIG. 31c).

[0114]FIGS. 32 and 33 show foil type subassemblies in a later stage ofcompletion, and FIG. 34 shows two of the sub-assemblies facing eachother across a space in which the beams are projected.

1. An optical fibre switching assembly comprising: (a) a first set ofoptical guides spaced from a second set of optical guides, and (b)respective steering devices for causing deflection of a beam of opticalradiation from a selected transmitting guide in the first set so that itis received by a selected receiving guide in the second set;characterised in that each of said devices comprises collimating meansfor collimating light from said transmitting guide and means for movingsaid collimating means or for causing relative movement between saidcollimating means and said transmitting guide to cause said deflection.2. An assembly according to claim 1, wherein said optical guide is anoptical fibre.
 3. An assembly according to claim 1, wherein saidcollimating means includes at least one lens having a focal plane.
 4. Anassembly according to claim 3, wherein said lens is spaced from the endof said guide.
 5. An assembly according to claim 3, wherein said lens isintegral with, or fixed to the end of said guide, whereby the guide andthe lens move together.
 6. An assembly according to claim 3 wherein thelens is fixed an end portion of a respective transmitting guide, wherebythe guide is moved to cause radiation, which exits from the fibre, tomove in the focal plane of said lens.
 7. An assembly according to claim3 wherein the end portion of the transmitting guide is fixed and therespective lens is moved, so that the focal point of the lens moves withrespect to me guide, whereby the radiation, which exits from the guideremains substantially within the focal plane of the lens.
 8. An assemblyaccording to claim 1, in which the steering device includeselectrostatic means for causing the movement.
 9. An assembly accordingto claim 1 in which the steering device includes a piezo electrictransducer for causing the movement.
 10. An assembly according to claim9 in which the piezo electric transducer is of a “foil type”, wherefingers of a comb-like array of piezo transducers are attached toactuating members, such as foil strips, for producing orthogonaldisplacement of the optical guide, or the lens, or both, whereby thefoils and combs can be assembled in a laminar matrix.
 11. An assemblyaccording to claim 9, where the piezo electric transducer is of a“monolithic type”, where the transducer is made of piezo electricmaterial, it has a body with a longitudinal axis, and the body hasconductive strips aligned with the longitudinal axis so as to definerespective portions of the transducer that impart respective transversemotions in different radial directions to provide a resultant motion inthe two dimensional plane perpendicular to the longitudinal axis;whereby a multiplicity of said bodies can be assembled in a columnarmatrix; the guide being aligned with said longitudinal axis, and eitherattached to said body, or received in a bore therein, whereby bending ofthe guide occurs with respect to the longitudinal axis, or the bodybeing attached to the collimating lens to cause it to move relative to afixed guide.
 12. An assembly according to claim 1 further includingposition sensing feedback means for sensing the amount of saiddeflection and for providing a feedback signal which is used in acontrol system for ensuring that the radiation from a transmitter guideis aimed at the correct receiver guide for making the required switchingconnection.
 13. An assembly according to claim 12 wherein capacitivechanges are sensed to determine position; the guide having a conductivecoating acting as at least one capacitor plate which moves with respectto at least one other fixed capacitor plate, thereby giving positionalinformation of either the guide or the collimating means.
 14. A assemblyaccording to claim 12 wherein the lens moves with respect to the guidewhich is fixed; the lens having a conductive coating acting as at leastone capacitive plate, at least one other capacitive plate being fixed toadjacent supporting structure.
 15. An assembly according to claim 12wherein conductive tracks are either on insulating boards arranged inlayers to form one set of the capacitive plates of the feedback system,or are provided as segments, the tracks crossing at points where pairsof conductive tracks, associated with individual guides or collimatingmeans, can be polled or addressed to detect capacitive changes.
 16. Anassembly according to claim 15 wherein a diagonal addressing system isused, wherein a signal is applied sequentially to diagonals of saidpoints, and capacitive changes are read sequentially from each row andcolumn,
 17. An assembly according to claim 11 in which the monolithictype of transducer co-operate with mechanical leverage means to magnifythe transducer movement before imparting motion to the guide or to thelens or both.
 18. An assembly according to claim 17 in which theleverage means includes a gimbal mounting, a flexure mounting, and anextension rod located between one end of the body of the transducer anda mounting point on the gimbal spaced from its pivotal axis.
 19. A piezoelectric transducer for use in a steering device for deflecting a beamin an optical switching assembly, the transducer being of a “foil type”,where fingers of a comb-like array of piezo transducers are attached toactuating members, such as foil strips, for producing orthogonaldisplacement of the optical guide, or the lens or both, whereby thefoils and combs can be assembled in a laminar matrix.
 20. A piezoelectric transducer for use in a steering device for deflecting a beamin an optical switching assembly, the transducer being of a “monolithictype” where the transducer is made of piezo electric material, it has abody with a longitudinal axis, and the body has conductive stripsaligned with the longitudinal axis so as to define respective portionsof the transducer that impart respective transverse motions in differentradial directions to provide a resultant motion in orthogonal axes;whereby a multiplicity of said bodies can be assembled in a columnarmatrix; the body either having a bore aligned with its longitudinal axisin which the guide can be received, whereby bending of the guide occurswith respect to the longitudinal axis, or the body being attached to thecollimating lens to cause it to move relative to a fixed guide.
 21. Atransducer according to claim 20 including mechanical leverage means tomagnify the transducer movement before imparting motion to the guide orto the collimating means.
 22. A transducer according to claim 21 inwhich the leverage means includes a gimbal mounting and an extension rodlocated between one end of the body of the transducer and a mountingpoint on the gimbal spaced from its pivotal axis.
 23. A sub-assembly forsensing capacitive changes to determine either the relative positions ofa guide and collimating means, or the position of a guide movingtogether with collimating means with respect to s fixed point; thesub-assembly including conductive tracks on insulating boards arrangedin layers to form one set of the capacitive plates of the feedbacksystem, or arranged in segments, the tracks crossing at points wherepairs of conductive tracks, associated with individual guides, can bepolled or addressed to detect capacitive changes.
 24. A sub-assembly ofa diagonal addressing system for use with a capacitive feedback sensingsystem wherein relative movement occurs between capacitive platesassociated optical guides or collimating lens and other capacitiveplates spaced from the guides, the guides being arranged in a matrix ofrows and columns, the subassembly farther including means for applying asignal sequentially to diagonals of said matrix and means for readingcapacitive changes sequentially from each row and column.